The present invention relates generally to combustion chambers for internal combustion engines, and more particularly, to a combustion chamber having a multi-zone construction.
In general, fuel injected engines include multiple cylinders that receive an atomized fuel injected into the cylinder. The fuel injector provides a fine mist of fuel that mixes with combustion generating gases, generally a mixture of fresh air and any remaining exhaust gases, within the cylinder. This mixture is then compressed and either spark ignited in gasoline engines, or compression ignited in diesel engines. While diesel engines may realize benefits from the present invention, it is primarily directed to fuel injected, spark ignited engines.
In this category of engines, the present invention is applicable to both two-cycle, or two-stroke, and four-stroke engines. Two-stroke engines are those engines that produce a power stroke with every rotation of the crank shaft. Direct fuel injected engines are those having a fuel injector arranged to inject fuel directly into the cylinder as opposed to port fuel injected engines that mix air and fuel before entry into the cylinder. Two-stroke engines are generally believed to be more prone to high exhaust emissions. The two-stroke engine industry, if it is to survive, must maximize efficiency and minimize the emissions to comply with governmental regulations. In the last few years, many advances have been made to advance two-stroke engines toward these goals. Since two-stroke engines are significantly lighter in weight than four-stroke engines, they have a distinct advantage. Recently, two-stroke engines, such as those incorporated into the EVINRUDE outboard motor and manufactured by the Assignee of the present invention, have resolved fuel efficiency concerns and reduced emissions to levels unheard of just a few years ago. Two-stroke engines now hold a distinct advantage over four-stroke engines. However, further advancement is desirable to further increase the desirability of two-stroke engines over four-stroke engines in various applications, such as those described above. Two-cycle engines that employ direct fuel injection will receive the most beneficial results with use of the present invention, however, other engines may benefit as well.
In order to improve the combustion process and reduce emission in the exhaust gases, it is desirable to obtain effective mixing and atomization of the fuel and combustion gas within the cylinder space. In so doing, it is desirable to prevent fuel from being accumulated on any surfaces of the combustion chamber. These surfaces include the face of the piston, the cylinder walls, and the area of the cylinder head enclosing the combustion chamber. Fuel accumulated on these surfaces is generally more difficult to ignite than atomized fuel mixed with air.
Fuel injected into the combustion chamber that is not thoroughly atomized and dispersed within the combustion chamber can create areas of uneven combustion. Areas of the combustion mixture having too little fuel lead to a lean burn and areas having too much fuel result in a rich burn. It is widely known that uneven burning combustion results in higher levels of pollutants in the exhaust gas as compared to the level of pollutants generated from a burn that is more fully atomized and dispersed within the spark zone.
Additionally, regions of high fuel concentration require more time for the fuel to burn as compared to areas where the fuel concentration is not as high which leads to inefficient use of the fuel. Often this time delay allows the temperature in the cylinder to drop to a point where the fuel is not readily burned. This type of uneven burning, as discussed above, leads to increased hydrocarbon and soot emissions from the engine. As such, it is important that the fuel injected into the combustion chamber not form regions of excessively high concentrations within the mixture.
These regions of high concentration are partially formed, in direct injection engines, by the proximity of the initial fuel spray to the walls of the combustion chamber. A fuel spray that is offset towards a wall of the combustion chamber experiences uneven mixing of the combustion gas and fuel spray. This uneven mixing detrimentally effects the entrainment, or mixing, of the combustion charge with the combustion gases and tends to result in increased engine emissions and decreased fuel efficiency.
Some direct injected engines focus a fuel spray into a dome formed concentrically in the cylinder head so that the fuel spray is positioned concentrically in the dome. This arrangement decreases the deposit of fuel on the combustion chamber walls of the dome but has a tendency to increase the amount of fuel impinged directly on the face of a piston in the combustion chamber. Additionally, having the fuel spray directed into the combustion chamber coaxially with the axis of reciprocation of the piston, while centering the combustion charge at ignition, also results in increased engine emissions. In two-stroke engines, by directing the fuel spray into the center of the combustion chamber increases the amount of unburned fuel that can exit the combustion chamber through the exhaust port. This unburned fuel increases the level of emissions discharged from the engine and reduces the fuel efficiency of the engine.
While the simple solution would be to tilt the spray in the cylinder head to face toward the intake port, doing so places the fuel spray closer to one side of the combustion chamber thereby increasing the potential for the fuel spray to be deposited on a wall of the combustion chamber. In order to maximize combustion efficiency, it would be preferable to burn the individual droplets of the fuel spray on the entire surface of the droplet. The droplets that are on or too close to the walls of the combustion chamber burn unevenly, and therefore, inefficiently. Also as discussed above, having the fuel spray passing through the combustion chamber closer to one wall than to another reduces the generation of a uniform combustion charge with maximized mixing of the fuel spray and the combustion gases.
It would therefore be desirable to have an engine with a combustion chamber arrangement that could receive a fuel mixture from a fuel injector and both provide a uniform spacing of the fuel spray from the walls of the combustion chamber and centralize a combustion charge in the combustion chamber for ignition.